Whether or not to Extract Defective First Permanent Molars at an Early Age
In children between 6 and 10 years of age, defective first molars can be an indication of inferior quality of all the permanent teeth. This inferior quality can be caused by imperfect formation of the dental tissues, an oral environment providing greater caries susceptibility, or both. In such cases the dentition can be maintained in a healthy state for a long period only if much care is taken of the teeth from an early age. Application of measures for caries prevention (sensible eating habits, good oral hygiene, and use of fluoride) and optimal professional dental care are of considerable importance. Procedures that might encourage caries and gingival disorders, such as use of orthodontic appliances, call for some restraint in their employment.
Besides inferior quality of all permanent teeth, isolated defective crown formation in first permanent molars can occur. Use of orthodontic appliances in such cases is less of a problem than where the deficiencies are general. The latter situation is usually seen when hypoplastic enamel occurs in the first permanent molars and in the incisors because of influences affecting these teeth when their formation is proceeding in more or less the same period.
When a child has very bad first permanent molars, consideration should be given to removing those teeth at an early age with the aim of obtaining the most satisfactory space closure. Extraction of the first permanent molars is then based primarily on the possibilities to influence the development of the dentition in such a way as to limit unfavourable effects. In that regard it is not only the time of the extraction that is important, but also the sequence used in removing first permanent molars in the two jaws.
This chapter begins by indicating the importance of the first permanent molars. After that follows discussion of the consequences of extraction and of some abnormal conditions, indications for and implications of extractions, and procedures involved in choosing the sequence of extractions. In addition, general guidelines are given.
17.2 The importance of first permanent molars
The first permanent molars are the teeth with the largest crowns and the largest root surface area. They are the principal teeth used in mastication. Moreover, they are essential in the development of the dentition and the coordination of facial growth.
They support the occlusion in a vertical direction and determine lower face height; during the second transitional period they are sometimes the only teeth that are in function. Further, their location largely determines the position that the premolars and other permanent molars will take up in sagittal direction after emerging. On top of this, the first permanent molars fulfill a significant role in the adjustment of the width of the maxillary dental arch to that of the mandibular one. Matching the transverse growth of the maxilla with the dimensions of the mandible is achieved by the good interdigitation of the first permanent molars together with other posterior teeth that solidly interdigitate in a buccolingual direction. A comparable situation exists in the coordination of anteroposterior growth of mandible and maxilla, in which the mesiodistal interdigitation is the important factor.223, 224 For these reasons, preservation of the first permanent molars is clearly desirable and from the above it may be seen that their early loss does not just affect the ability to chew.
One of the objectives to be considered in choosing the least unfavourable moment for extraction of the first permanent molars is to limit if not entirely eliminate the period during which interdigitation is inadequate. Thus, extraction of the first permanent molars at the age of 7 years in a case of marked attrition of the deciduous molars leads to a significant period of inadequate interaction between the jaws of the kind mentioned above.
17.3 Consequences of extracting first permanent molars
It occasionally happens in orthodontics that expectations are not fulfilled, and that applies also to the consequences of extracting first permanent molars at an early age. In this discussion, however, it will be assumed for didactic purposes that the original expectations should be achieved.
At every patient visit one should check to what extent the development conforms to expectations. The situation in the mouth should be compared with the initial conditions, which preferably have been recorded with good plaster models. Systematic examination of and thought about the changes in both dental arches and the occlusion, in particular bearing on the second permanent molars, will provide the information needed to show whether or not everything is going as planned. If not, intervention can be undertaken according to what is necessary for that patient.
17.3.1 Migration, tipping, and rotation of adjacent teeth
Extracting teeth results in migration of adjacent teeth. Migration in this context refers to movement within the jaw before emergence as well as movement of teeth in the dental arch after emergence. Migration often is associated with tipping and sometimes with rotation around the long axis of the tooth.
Extraction of the first permanent molars leads to mesial (and occlusal) migration of the second permanent molar and distal migration of the premolars (Fig. 17-1). The second permanent molars not only tip mesially, they rotate mesiolingually as well.
Figure 17-1
Fig. 17-1 Development of the dentition when first permanent molars in both jaws are extracted in otherwise normal cases. The drawings A, B, and C reproduce the situation shortly before extraction. In the adjacent drawings D, E, and F, the conditions are shown as they would be expected to exist some years later.
A At age approximately 10 years, the occlusal marginal ridges of the second molars are still about one crown height away from the occlusal plane. Their bifurcations have already formed. When the third molars are present the crown formation is already proceeding.
B Spacing is present between the maxillary incisors. The buccal surfaces of the first permanent molars are farther buccally than those of the second deciduous molars.
C No spaces are present in the mandible. The teeth are positioned harmoniously in the line of the arch.
D Some years after extraction of the first permanent molars the mandibular second permanent molars have tipped mesially and only the distal part of their occlusal surfaces contacts the maxillary molars. The latter are also tipped mesially, though to a lesser extent. The third molars have moved mesially within the jaws and will probably emerge without problems. This is fairly certain for the maxilla but not for the mandible. Sometimes the mandibular premolars, and particularly the second premolars, are tipped distally. Diastema-ta are present in the posterior regions; these are larger in the mandible than in the maxilla.
E In the maxilla the second permanent molars not only have migrated mesially, they have also rotated markedly mesiopalatally more or less around an imaginary axis through the palatal root and the mesiopalatal cusp. The second premolars have drifted distally and moreover have rotated distopalatally. The first premolar has also been displaced distally, usually without significant rotation.
F In the mandible the second permanent molar has been displaced less mesially than in the maxilla. The rotation that has occurred is more limited. In the mandible the premolars move more distally after extraction of first permanent molars than in the maxilla. There is also more distolingual rotation by the mandibular second premolars than by the maxillary ones. Further, a similar rotation can be seen in the mandibular first premolars, though to a lesser extent than in the mandibular second premolars.
There is a difference between mandibular and maxillary teeth in the degree of migration, tipping, and rotation that follows extraction of first permanent molars. This difference is related to the diversity in development of the molar regions in both jaws. In the mandible, before the second and third molars emerge they are oriented with their crowns mesially and lingually inclined. In the maxilla, however, the second and third molars before emergence have their crowns inclined distally and buccally.
After extraction of a maxillary first permanent molar, the adjacent erupting second permanent molar performs a tipping movement in which the crown moves more mesially than the apices. This movement corresponds more or less with the normal changes in mesiodistal angulation that an erupting second permanent molar would experience if the first one had not been extracted at an early age. The tipping movement is, however, a little greater.
A considerably more unfavourable situation exists in that respect in the mandible. Under normal circumstances a second permanent molar that originally was mesially inclined would upright itself on eruption. Extracting the first permanent molar affects the eruption path of the not yet emerged second molar, which subsequently will display little or no uprighting movement, or even will tip more mesially. This last movement is the opposite to what is required to achieve an acceptable angulation after emergence.
In contrast to the mandibular teeth, the maxillary second permanent molars in the absence of the first permanent molars show only a slight abnormality in mesiodistal angulation. To reach a good mesiodistal angulation the root apices of the maxillary molars do not need to move so far mesially as those in the mandible.12, 192 It also makes a difference how far the eruption of the second permanent molars has progressed at the time the first permanent molars are extracted. A second permanent molar that has not yet emerged will migrate mesially in the jaw when the adjacent first molar is removed. It will then emerge farther mesially than it otherwise would have done. The degree to which it emerges mesially will depend on the time span between extraction of the first permanent molar and the moment of emergence of the second molar. The longer the interval the greater the mesial drifting will be. The extent to which the second permanent molar will tip after extraction of the first depends on the spatial conditions in the jaw, the original orientation of the second molar, and its pattern of eruption. For both jaws, if one waits until the second permanent molar has emerged before extracting the first molar, the second molar subsequently will end up in a more mesially tilted position than it would have if the extraction had been executed a year earlier.
The mesiolingual rotation of the second permanent molar after extraction of the first molar is more pronounced in the maxilla than the mandible. Maxillary second permanent molars rotate about an axis more or less through the mesiopalatal cusp and the palatal root. Mandibular second molars also rotate mesiolingually, but less so. This distinction can be attributed to the conformation of the roots and the morphology of the investing structures of the respective jaws.
17.3.2 Closing spaces and changes in occlusion
After extracting the first permanent molars the adjacent second molars drift more mesially in the maxilla than in the mandible. The space resulting from the removal of the maxillary first permanent molar is eliminated more or less completely by this reaction. The maxillary premolars move distally only slightly so that the larger part of the space reduction is accomplished by mesial migration of the maxillary second permanent molar. In the mandible diastemata often remain, even though the mandibular premolars migrate more distally than those in the maxilla.158, 159 Further, the mandibular premolars rotate more distolingually than the maxillary premolars, whereas in both jaws this rotation is more marked for the second premolars than for the first premolars.
Extraction of first permanent molars at a young age leads to an earlier emergence of the second and third permanent molars.55 The effect on the overjet is only minor. The mandibular and maxillary incisors become a little more upright, the interincisal angle increases a little. The effect on the facial profile is also limited; the lips usually only fall back insignificantly.131, 212
The mesial tipping of the second permanent molars (especially in the mandible), their mesial drifting and rotation (especially in the maxilla), and the distal tipping and rotation of the premolars (especially in the mandible), lead to a ramshackle occlusion. Both transversely and sagittally, good interdigitation is lacking. Normally the situation improves over the years and a more favourable occlusion develops. A really good occlusion, however, is almost never achieved, essentially because the mandibular second molar seldom uprights sufficiently. From a periodontal point of view the situation between the second premolar and the second permanent molar (particularly in the mandible) usually remains unsatisfactory because of that lack of uprighting.
The changes indicated above that result from the loss of a first permanent molar at an early age apply to otherwise normal circumstances (Fig. 17-1). If there is crowding or spacing, a non-Class I situation, no normal lip relationship, and/or a deviating function, the changes will often present themselves in a different form.
17.4 Consequences of anomalous conditions
After outlining the consequences of extracting the first permanent molars in a normal dental situation, consideration will follow of the results of such extractions in anomalous conditions. In addition, a number of side effects will be detailed.
Consequences of early loss of the four first permanent molars are not as bad in situations of crowding as in those of spacing (Fig. 17-2).81, 211 Where crowding is concerned, it is noted that especially in the mandible more space becomes available for rotated or overlapping incisors and canines, as a result of distal drifting of premolars. In the maxilla this is less evident. Extraction of a maxillary permanent molar provides only limited space gain for a permanent canine that is emerging labially.
Figure 17-2
Fig. 17-2 Development of the dentition when all first permanent molars are extracted at an early age in a patient with crowding in both jaws. The drawings A, B, and C reproduce the situation after the second deciduous molars have already been lost prematurely and shortly before the first permanent molars are to be removed. In the adjacent drawings D, E, and F, the conditions are shown as they would be expected to exist after a few years.
A Because of the earlier premature loss of the second deciduous molars the first permanent molars have already drifted and tilted mesially, more in the mandible than in the maxilla. Also, the second permanent molars, which are still within the alveolar processes, have moved slightly mesially. The premolars and permanent canines are closer to each other than when there is more space available in both jaws (compare with Fig. 17-1).
B Crowding in the maxilla is partly caused by premature loss of the deciduous molars. The first permanent molars have migrated and rotated mesially.
C Some crowding also exists in the mandibular arch. The first permanent molars have migrated mesially.
D Some years after extraction of the first permanent molars and completion of the transition, the second permanent molars have reached a reasonable sagittal occlusion. The inter-digitation is not optimal. The mesial cusps of the opposing second permanent molars do not occlude adequately. Both second molars, mandibular more than maxillary, are tilted mesially. In accordance with the initial crowding, all spaces in both arches are now closed. The premolars interdigitate reasonably well. They exhibit no abnormal mesiodistal inclination.
E The limited distal migration of the premolars provided some extra room for improvement of the positions of the incisors/>
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